TY - JOUR

T1 - Stability and ordering of bcc and hcp TiAl+Mo phases: An ab initio study

AU - Dehghani, Mohammad

AU - Ruban, Andrei V.

AU - Abdoshahi, Neda

AU - Holec, David

AU - Spitaler, Jürgen

N1 - Publisher Copyright: © 2021

PY - 2022/1/18

Y1 - 2022/1/18

N2 - Atomic ordering in bcc and hcp TiAl+Mo alloys near equiatomic TiAl composition is investigated by different ab initio tools. We show that small addition of Mo, about 5 at. %, is enough to make bcc alloys with more than 50 at. % of Ti stable with respect to the hcp alloys. Moreover, such alloying also leads to stabilizing the B2 ordered structure with respect to its B2 2 modification, which is the bcc-based ground state structure of binary TiAl. The site preference of Mo in the B2 and B19 ordered alloys is investigated by different methods: in the dilute limit, using the transfer energy formalism; in concentrated alloys, from the total energies of disordered and partially ordered alloys in the mean-field coherent potential approximation; and from Monte Carlo simulations. These methods produce consistent results for the B2 phase predicting a strong preference of Mo to Al sublattice. The site preference of Mo in the B19 phases varies from a weak preference for Al sites in the single impurity calculations to a quite strong preference for Ti sites in the mean-field approximation and finally to a strong Al preference in Monte Carlo simulations. Mo alloying dramatically increases the order–disorder transition temperatures in bcc and hcp Al-deficient Ti 0.5Al 0.5−xMo x alloys.

AB - Atomic ordering in bcc and hcp TiAl+Mo alloys near equiatomic TiAl composition is investigated by different ab initio tools. We show that small addition of Mo, about 5 at. %, is enough to make bcc alloys with more than 50 at. % of Ti stable with respect to the hcp alloys. Moreover, such alloying also leads to stabilizing the B2 ordered structure with respect to its B2 2 modification, which is the bcc-based ground state structure of binary TiAl. The site preference of Mo in the B2 and B19 ordered alloys is investigated by different methods: in the dilute limit, using the transfer energy formalism; in concentrated alloys, from the total energies of disordered and partially ordered alloys in the mean-field coherent potential approximation; and from Monte Carlo simulations. These methods produce consistent results for the B2 phase predicting a strong preference of Mo to Al sublattice. The site preference of Mo in the B19 phases varies from a weak preference for Al sites in the single impurity calculations to a quite strong preference for Ti sites in the mean-field approximation and finally to a strong Al preference in Monte Carlo simulations. Mo alloying dramatically increases the order–disorder transition temperatures in bcc and hcp Al-deficient Ti 0.5Al 0.5−xMo x alloys.

UR - http://www.scopus.com/inward/record.url?scp=85122960808&partnerID=8YFLogxK

U2 - 10.1016/j.commatsci.2021.111163

DO - 10.1016/j.commatsci.2021.111163

M3 - Article

VL - 205.2022

JO - Computational materials science

JF - Computational materials science

SN - 0927-0256

IS - 1 April

M1 - 111163

ER -